Medical robotic systems such as those used in performing minimally invasive surgical procedures offer many benefits over traditional open surgery techniques, including less pain, shorter hospital stays, quicker return to normal activities, minimal scarring, reduced recovery time, and less injury to tissue. Consequently, demand for medical robotic systems used for performing such minimally invasive surgical procedures is strong and growing.
Examples of medical robotic systems include the daVinci® Surgical System and the daVinci® S™ Surgical System from Intuitive Surgical, Inc., of Sunnyvale, Calif. Each of these systems includes a surgeon's console, a patient-side cart, a high performance three-dimensional (“3-D”) vision system, and Intuitive Surgical's proprietary EndoWrist™ articulating surgical instruments or tools, which are modeled after the human wrist so that when added to the motions of the robotic arm assembly holding the surgical instrument or tool, they allow at least a full six degrees of freedom of motion, which is comparable to or even greater than the natural motions of open surgery.
In such a system, a patient-side cart typically has three or more robotic arm assemblies each having a slave manipulator for holding and manipulating a medical device such as a surgical tool or image capturing device for performing or viewing a medical procedure at a surgical site within a patient. To manipulate these medical devices, the surgeon's console also includes master manipulators which may be selectively associated with the slave manipulators holding them. Typically, two such master manipulators are provided, one for each hand of the operating surgeon.
Precise control in the positioning and manipulation of the surgical tools and their end effectors is important for performing successful medical procedures on patients. Linkages coupling joint actuators to driven joints of the surgical tools or their manipulators are generally fairly rigid so that surgical tool positions and velocities, and in particular, those of their end effectors, may be reasonably and quickly estimated in such medical robotic systems by applying kinematic transforms to sensed positions, velocities, accelerations, or torques of the actuators. However, when linkages are characterized by non-idealities such as cable friction, hysteresis and compliance, tool positions determined by applying kinematic transforms to sensed positions, velocities, accelerations, or torques of the actuators may result in excessive estimation errors in the end effector positions and consequently, diminished control capability for a surgeon performing a medical procedure.
Furthermore, the compliance and friction of the cable transmission affect the way the torques propagate from motors to the end effectors of the surgical tools. The capability of performing surgical procedures or gestures that require a fine control over the forces and torques applied by the end effectors of the surgical tools on the manipulated tissues or objects (e.g. suturing), is thus diminished.